text: While lists of noble metals can differ, they tend to cluster around the six platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum) plus gold.
  In addition to this terms function as a compound noun, there are circumstances where noble is used as an adjective for the noun metal'.  A galvanic series is a hierarchy of metals (or other electrically conductive materials, including composites and semimetals) that runs from noble to active, and allows one to predict how materials will interact in the environment used to generate the series. In this sense of the word, graphite is more noble than silver and the relative nobility of many materials is highly dependent upon context, as for aluminium and stainless steel in conditions of varying pH.
  The term noble metal can be traced back to at least the late 14th century and has slightly different meanings in different fields of study and application.
  Prior to Mendeleev's publication in 1869 of the first (eventually) widely accepted periodic table, Odling published a table in 1864, in which the "noble metals" rhodium, ruthenium, palladium; and platinum, iridium, and osmium were grouped together, and adjacent to silver and gold.